The present invention relates to an apparatus and a method for stabilizing a vehicle combination made up of a tractor vehicle and a trailer or semitrailer.
German Published Patent Application No. 25 47 487 describes an apparatus for stabilizing a vehicle that comprises a leading element and a towed element. The towed element is joined via a linkage to the leading element. The apparatus has a transducer for sampling the inflection angle between the leading element and towed element. A transducer is also provided to sense the steering angle. The apparatus comprises an analysis circuit to which the signals of both transducers are conveyed and which generates output signals if the inflection angle exceeds specific angular variables that depend on the steering angle. The specific angular variables correspond to the inflection angles determined as a function of the steering angle and permissible in the respective driving situation. In addition, the apparatus provides for a device, for automatically applying brake pressure to at least one axle of the towed element, which is actuated by the output signals of the analysis circuit. By way of the braking action, the operation described above causes the vehicle to stretch out, thus decreasing the instantaneous inflection angle.
An object of the present invention is to improve existing apparatuses and methods for stabilizing a vehicle combination.
Since their introduction, the use of brake slip control systems to prevent accidents in critical longitudinally dynamic driving situations has become more and more widespread. Such brake slip control systems are available both for passenger cars and for commercial vehicles. For quite some time, driving safety for passenger cars has been additionally improved with a so-called vehicle dynamics control system. A vehicle dynamics control system of this kind is used to control the yaw rate of the vehicle. Vehicle dynamics control systems not only offer the driver improved basic functionality in terms of brake slip and drive slip control, but also provide him or her with active assistance in critical transversely dynamic situations. Vehicle stability is thereby improved in all operating situations, i.e. in the full and partial braking range, when coasting, under power, and in response to load changes. The vehicle dynamics control system engages as soon as the vehicle-dynamics limit region is reached. In passenger cars, the vehicle dynamics control system reduces the risk of a spin even in extreme steering maneuvers, and allows the vehicle to be controlled safely.
The advantages of a vehicle dynamics control system are also to be made available for commercial vehicles. For commercial vehicles, however, the requirements in terms of stability are not limited simply to the spin characteristics of a single vehicle element; instead, inflection of the members of a multi-part vehicle must also be taken into account. The apparatus according to the present invention is an apparatus for stabilizing a vehicle combination comprising a tractor vehicle and a trailer or semitrailer. Because of its widespread use for road transport of goods, and the particular problems of tractor-trailer units, in the exemplary embodiment the apparatus according to the present invention is presented for a vehicle combination comprising a tractor vehicle and a semitrailer. Irrespective of this, the apparatus according to the present invention can also be used for a vehicle combination that comprises a tractor vehicle and a trailer, in particular a drawbar trailer. In vehicle combinations, a hazardous situation occurs as soon as the inflection angle between tractor vehicle and semitrailer or trailer becomes too great.
The apparatus according to the present invention contains a first determination arrangement which is used to determine an inflection angle variable that describes the angle between an axis oriented in the longitudinal direction of the tractor vehicle, in particular the longitudinal axis of the tractor vehicle, and an axis oriented in the longitudinal direction of the trailer or semitrailer, in particular the longitudinal axis of the trailer or semitrailer. The apparatus also contains a processing arrangement with which a comparison is made as a function of the inflection angle variable and a comparison variable. The apparatus also has a first actuator arrangement which is associated with the trailer or semitrailer and with which a brake pressure can be established at at least one wheel of the trailer or semitrailer. These first actuator arrangement is actuated at least as a function of the comparison performed with the processing arrangement.
According to the present invention, the apparatus contains a second determination arrangement with which the comparison variable is determined as a function of a velocity variable that describes the velocity of the tractor vehicle, and/or as a function of whether stability interventions are being performed for the tractor vehicle.
The determination according to the present invention of the comparison variable as a function of the velocity variable is made because the velocity of the vehicle combination influences the stability of the vehicle combination to a considerable degree. If the vehicle combination has a low velocity (as is the case, for example, during a parking maneuver), a large comparison variable can be permitted for the inflection angle. Because of the low kinetic energy of the semitrailer, an increase in the inflection angle - such as might occur, for example, by possible pushing of the semitrailer during a braking operation - and thus instability of the vehicle combination, are not to be expected. If, on the other hand, the velocity of the vehicle combination is high (as is the case, for example, during highway driving), a comparison variable that is smaller than in the case of a parking maneuver must be defined for the inflection angle. If too great an inflection angle were permitted while traveling at high velocity, a transverse dynamic influence on the semitrailer, because of its high kinetic energy, could result in an uncontrolled increase in the inflection angle and thus in jackknifing of the vehicle combination. Against this background, it is clear that a preset comparison variable that has a high value, such as is necessary, for example, for a parking maneuver, cannot be used. Too great a comparison variable would result in poor stability at higher vehicle velocities, since potential instabilities would be detected too late, and thus the first actuator arrangement would be actuated too late.
The reason why the comparison variable is determined as a function of whether stability interventions are being performed for the tractor vehicle is that if stability interventions are being performed for the tractor vehicle, instability of the vehicle combination may be expected. Since stability interventions on the tractor vehicle result, inter alia, in a reduction in the velocity of the tractor vehicle, the inflection angle allowed should not be too great in such a case, since in such cases it could result in an increase in the inflection angle and thus in instability of the vehicle combination.
The aforementioned stability interventions for the tractor vehicle are advantageously those that are performed at least as a function of a variable describing the transverse dynamics of the tractor vehicle, in particular a variable describing the yaw rate and/or the transverse acceleration of the tractor vehicle. These variables are usually controlled in the vehicle dynamics control systems mentioned earlier. Alternatively or additionally, the stability interventions for the tractor vehicle are also performed as a function of wheel behavior variables which describe the wheel behavior of the wheels of the tractor vehicle or semitrailer. The wheel behavior variables are, for example, wheel rotation speed variables or slip variables.
In order to implement the stability interventions that are performed for the tractor vehicle, the apparatus has two actuator arrangements that are associated with the tractor vehicle. These stability interventions are, advantageously, interventions on the brakes of the tractor vehicle and/or on the propulsion system of the tractor vehicle and/or on the retarder of the tractor vehicle. The primary result of the interventions on the propulsion system or on the retarder is to reduce the velocity of the tractor vehicle. It is possible by way of the interventions on the brakes of the tractor vehicle on the one hand to apply to individual wheels, in controlled fashion, braking torques which result in a yaw moment about the vertical axis of the tractor vehicle. On the other hand, the interventions on the brakes of the tractor vehicle can also be used to reduce its velocity.
Since the comparison variable is determined in the second determination arrangement as a function, inter alia, of whether stability interventions are being performed for the tractor vehicle, a corresponding datum must be delivered to the second determination arrangement. Two advantageous embodiments are possible for this. On the one hand, variables that are generated in the processing arrangement for activating the second actuator arrangement are delivered to the second determination arrangement. These variables are, for example, variables as a function of which interventions are performed on the brakes of the tractor vehicle and/or on the propulsion system and/or on the retarder. On the other hand, the variable delivered to the second determination arrangement is one which is generated in the processing arrangement and which indicates that stability interventions are being performed for the tractor vehicle. This variable indicates globally that stability interventions are being performed, but without containing any information as to what kinds of stability interventions are being performed.
It has proven to be particularly advantageous that the comparison variable is moreover determined as a function of a steering angle variable that describes the steering angle established for the tractor vehicle. Taking the steering angle variable into account when determining the comparison variable makes possible, for example, better detection of a parking maneuver. The apparatus provides for third a determination arrangement for determining the steering angle variable.
The first actuator arrangement are advantageously actuated if the inflection angle variable is greater than the comparison variable, since instability of the vehicle combination may be expected in such situations.
The comparison variable is advantageously a defined comparison variable. There are two possibilities in this context: on the one hand, the comparison variable can be a predefined comparison variable that is determined beforehand using driving tests and by observation of the vehicle""s behavior. On the other hand, the comparison variable can be one that is determined during operation of the vehicle with the aid of a first vehicle model. The first vehicle model can, for example, be selected in such a way that the comparison variable is determined as a function of the steering angle established by the driver and the vehicle velocity. The defined comparison variable is adapted to the particular existing vehicle combination situation as a function of the velocity variable and/or as a function of whether stability interventions are being performed for the tractor vehicle. In the first case, in which the comparison variable is predefined, adaptation of the comparison variable is performed in equal measures as a function of the velocity variable and as a function of whether stability interventions are being performed for the tractor vehicle. In the second case, in which the comparison variable is determined with the aid of a first vehicle model, adaptation of the comparison variable as a function of whether stability interventions are being performed for the tractor vehicle is of greater importance, since the vehicle velocity is already taken into account due to the use of the first vehicle model.
The term xe2x80x9cvehicle combination situationxe2x80x9d will be discussed at this point. The xe2x80x9cvehicle combination situationxe2x80x9d is to be understood as the particular existing instantaneous situation, or the particular existing instantaneous state, of the vehicle combination. In other words, the term xe2x80x9cvehicle combination situationxe2x80x9d describes whether or not the vehicle combination is jackknifed, whether or not an element of the vehicle combination is unstable, or whether or not the vehicle combination as such is unstable.
In view of the above considerations, the value of the predefined comparison variable is advantageously reduced as the value of the velocity variable increases, and/or in the presence of stability interventions performed for the tractor vehicle.
It has proven to be particularly advantageous that the value of the predefined comparison variable, once it has been reduced, is maintained for a specific period of time. This ensures that, for example in the case in which the comparison variable has been reduced because of stability interventions performed for the tractor vehicle, it is additionally maintained for a specific period of time after those stability interventions, thus preventing potential instabilities in the vehicle combination.
It has also proven to be advantageous that the value of the comparison variable is read out from a characteristics diagram as a function of the value of the velocity variable and/or as a function of the nature and or intensity of the stability interventions performed for the tractor vehicle. With this type of determination, the value of the comparison variable correspondingly decreases as the value of the velocity variable becomes greater and/or in the presence of stability interventions performed for the tractor vehicle. The value pairs stored in the characteristics diagram are determined, for example, beforehand by way of driving tests.
Advantageously, the first determination arrangement is configured as a sensor arrangement. A possible sensor arrangement is, for example, a potentiometer in effective connection both with the tractor vehicle and with the semitrailer, or optical sensors, or ultrasonic sensors, or radar sensors. Alternatively, it is advantageous if the inflection angle variable is determined in the first determination arrangement with the use of a second vehicle model. In this context it is important to ensure, however, that the second vehicle model uses input variables different from those for the first vehicle model.